1. Field of the Invention
The present invention relates to an image forming apparatus, a method of forming an image, and an image forming system, which form an image on a sheet based on a job.
2. Description of the Related Art
A copying machine, a facsimile, a printer, or a multifunction machine provided with multi-functions thereof sequentially conveys sheets inside the machine, forms an image on a sheet, and discharges the sheet, and is based on the premise that the sheets are smoothly conveyed through a sheet feeding tray, or the like. A conveyance state of the sheets is grasped with various sensors. When a jam of a sheet is detected by the sensors, conveyance of the sheet is stopped, and sheets remaining inside the machine are discharged.
For example, JP 2008-52125 A discloses that, when a jam of a sheet occurs, sheets physically conveyable to a discharge destination are continuously conveyed and purged, and non-conveyable sheets are automatically purged after removal of the jammed sheet.
Further, JP 2006-343727 A discloses that, when a jam occurs in a single-sided/double-sided common path, purge through a double-sided dedicated path is performed after the jam is handled, and when a jam occurs in the double-sided dedicated path, purge through the double-sided dedicated path is performed after the jam is handled.
By the way, there are problems that, in an image forming apparatus, the number of sheets conveyed inside the machine is increased in accordance with improvement of performance and an increase in size, and once a jam of a sheet occurs, it takes much time to handle the jam, and it becomes difficult to discharge a large number of sheets depending on a portion where the jam has occurred and more time is required for recovery.
For example, conventional sheet conveyance control has a structure in which, when sheets subjected to image formation are sent out to a post-processing unit or to a sheet discharge unit, normal conveyance cannot be performed if the sheets are not sent out in an original discharge order. Meanwhile, when an unusable sheet purge function is implemented, the function being to discharge unusable sheets remaining inside the machine to an outside of the machine using a conveyance path at the time of occurrence of a jam, discharge may not be performed in the original order in which the sheets are supposed to be discharged, depending on a print mode or a position where the jam has occurred.
Example A) A missing page due to a jam in a conveyance unit with branching/merging of post-processing, a paper inserter, and the like.
Example B) Single-sided printed/double-sided printed sheets mixed in a circulation path at the time of double-sided printing.
Therefore, there is a problem that, under control of conventional sheet conveyance, a physically conveyable unusable sheet needs to be manually removed in a state where the device is stopped. Further, there is a problem that sheet conveyance control specific to unusable sheet purge needs to be implemented separately from the conveyance of usable sheets.